This invention relates to a method for preparing novel polymeric acetal carboxylates useful as complexing agents and detergency builders.
The property possessed by some materials of improving detergency levels of soaps and synthetic detergents and the use of such materials in detergent compositions is known. Such cleaning boosters are called "builders" and such builders permit the attainment of better cleaning performance than is possible when so-called unbuilt compositions are used. The behavior and mechanisms by which builders perform their function are only partially understood. It is known that good builders must be able to sequester most of the calcium and/or magnesium ions in the wash water since these ions are detrimental to the detergency process. However, it is difficult to predict which class of compounds possess useful combinations of builder properties and which compounds do not because of the complex nature of detergency and the countless factors which contribute both to overall performance results and the requirements of environmental acceptability.
Sodium tripolyphosphate (STP) has been found to be a highly efficient cleaning and detergent builder and this compound has been widely used for decades in cleaning and detergent formulations. Indeed, millions of pounds of STP are used each year in cleansing formulations because of its superior builder qualities. However, because of the recent emphasis on removing phosphates from detergent and cleaning compositions for environmental reasons, the detergent and cleaning industry is now looking for materials suitable for use as builders which do not contain phosphorus, and which are environmentally acceptable.
Such a material and its use in detergent compositions has been disclosed in copending applications Ser. Nos. 826,424 filed Aug. 22, 1977, 826,426 filed Aug. 19, 1977 and 826,425 filed Aug. 22, 1977. A preferred method for making such polymeric acetal carboxylates is disclosed in application Ser. No. 844,566 filed Nov. 21, 1977. The polymeric acetal carboxylate salts described in the above applications were tested for sequestration function using the procedures described by Matzner et al. in "Organic Builder Salts as Replacements for Sodium Tripolyphosphate", TENSIDE DETERGENTS, 10, No. 3, pages 119-125 (1973). The sequestration of calcium ions and magnesium ions as a percent of STP performance as a function of the number of repeating acetal carboxylate units showed that when the polymeric acetal carboxylate salts averaged 130 repeating units, the polymeric salt had a performance of 172 percent of STP. Thus, such polymeric acetal carboxylate salts were found to be superior detergent builders and were stable under home laundry use conditions, but depolymerized at lower pH, making them more readily biodegradable.
Although satisfactory performance was achieved using the polymeric acetal carboxylates prepared by the procedures described in the above-identified applications, the polymeric acetal carboxylate prepared by such procedures frequently required as much as 24 hours to saponify the ester of the polymeric acetal carboxylate to the corresponding alkali metal salt. Furthermore, the metal salt frequently was discolored due to impurities formed during the preparation of the polymeric acetal carboxylate.
Now, according to the present process, the polymeric acetal carboxylate ester can be saponified to the corresponding alkali metal salt in less than two hours and by the preferred procedure of the process of the present invention, the impurities which caused some discoloration in the resulting polymeric alkali metal salt can be removed. Thus, the resulting polymeric acetal carboxylate salt can be provided in higher purity that is more esthetically appealing and in a much shorter time than the methods used in the above-identified applications.